In order of decreasing abundance the major gases in the sea are nitrogen, oxygen, carbon dioxide and

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In order of decreasing abundance the major gases
in the sea are nitrogen, oxygen, carbon dioxide
and the noble gases, argon (Ar), neon (Ne) and
helium (He).
Dissolved Gases in the Ocean

• Nitrogen and the noble gases are considered to be
  inert because they are chemically non-reactive.

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The solubility and saturation value for gases in
sea water increase as temperature and salinity
decrease and as pressure increases.

• Solubility is the ability of something to be
  dissolved and go into solution.
• Saturation value is the equilibrium amount of gas
  dissolved in water at an existing temperature,
  salinity and pressure.
• Water is undersaturated when under existing
  conditions it has the capacity to dissolve more
  gas. Gas content is below the saturation value.

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P pressure V volume of gas n number of
moles of gas present T absolute temp. K ( C
273.15) R gas constant
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Henrys Law G HG x pp(G) G concentration
of gas G in solution Pp(G) partial pressure of
the gas HG Henrys law constant for gas G, this
is a function of temp. and salinity
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• The surface layer is usually saturated in
  atmospheric gases because of direct exchange with
  the atmosphere.
• Below the surface layer, gas content reflects
  relative importance of respiration,
  photosynthesis, decay and gases released from
  volcanic vents.

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Oxygen tends to be abundant in the surface layer
and deep layer bottom, but lowest in the
pycnocline.

• Surface layer is rich in oxygen because of
  photosynthesis and contact with the atmosphere.
• Oxygen minimum layer occurs at about 150 to 1500m
  below the surface and coincides with the
  pycnocline.
• Sinking food particles settle into this layer and
  become suspended in place because of the greater
  density of the water below.
• The food draws large numbers of organisms which
  respire, consuming oxygen.

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5-6

• Decay of uneaten material consumes additional
  oxygen.
• Density difference prevents mixing downward of
  oxygen-rich water from the surface or upwards
  from the deep layer.
• The deep layer is rich in oxygen because its
  water is derived from the cold surface waters
  which sank (convect) to the bottom. Consumption
  is low because there are fewer organisms and less
  decay consuming oxygen.
• Anoxic waters contain no oxygen and are inhabited
  by anaerobic organisms (bacteria).

Gases in Seawater
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Apparent Oxygen Utilization (AOU)
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Carbon dioxide is of major importance in
controlling acidity in the sea water.
5-6

• Major sources of carbon dioxide are respiration
  and decay.
• Major sinks are photosynthesis and construction
  of carbonate shells.
• Carbon dioxide controls the acidity of sea water.
• A solution is acid if it has excess H
  (hydrogen) ions and is a base if it has excess
  OH- (hydroxyl) ions.
• pH measures how acid or base water is.
• - pH of 0 to 7 is acid.
• - pH of 7 is neutral.
• - pH of 7 to 14 is base.

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Gases in Seawater

• pH is related to the amount of CO2 dissolved in
  water because it combines with the water to
  produce carbonic acid which releases H ions.
• CO2 H2O ?? H2CO3 ?? H HCO3-?? H CO3-2
• H2CO3 is carbonic acid, HCO3- is the bicarbonate
  ion and CO3-2 is the carbonate ion.
• Changing the amount of CO2 shifts the reaction to
  either the right or left of the equation.
• Adding CO2 shifts the reaction to the right and
  produces more H ions making the water more acid.
• Removing CO2 shifts the reaction to the left,
  combining H ions with carbonate and bicarbonate
  ions reducing the acidity.

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Dissolved CO2 in water acts as a buffer, a
substance that prevents large shifts in
pH. Dissolution of carbonate shells in deep water
results because cold water under great pressure
has a high saturation value for CO2 and the
additional CO2 releases more H ions making the
water acid. Warm, shallow water is under low
pressure, contains less dissolved CO2 and is less
acidic. Carbonate sediments are stable and do not
dissolve.
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The sea surface microlayer is the water surface
to a depth of a few hundred micrometers. It is
critical for the exchange (i.e., gases) between
the atmosphere and the ocean.
The Ocean Sciences Sea Surface Microlayer
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The Ocean Sciences Sea Surface Microlayer

• Processes within the microlayer can be divided
  into the
• Biological - bacteria and plankton are much more
  abundant in the layer than below.
• Photochemical effect - the interaction of
  ultraviolet light and organic compounds.

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Neuston layer is the habitat of the sea surface
microlayer and is inhabited by the neuston, all
organisms of the microlayer. Processes that
transport matter to the surface layer from below
are Diffusion - random movement of
molecules. Convection - vertical circulation
resulting in the transfer of heat and
matter. Bubbles - the most important process
because bubbles absorb material and inject it
into the air as they bursts.
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Nutrients are chemicals essential for life.
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• Major nutrients in the sea are compounds of
  nitrogen, phosphorus and silicon.
• Because of usage, nutrients are scarce at the
  surface and their concentrations are measured in
  parts per million (ppm).
• Concentration of nutrients vary greatly over time
  and because of this they are considered a
  non-conservative property of the sea.

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Trace elements occur in minute quantities and are
usually measured in parts per million (ppm) or
parts per billion (ppb).
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Water Molecule

• Even in small quantities they are important in
  either promoting life or killing it.

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He- Distribution
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Iron Fertilization Experiments
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Commercial Interests?
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Amount of light entering the ocean depends upon
the height of the sun above the horizon and the
smoothness of sea surface.
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• 65 of light entering the ocean is absorbed
  within the first meter and converted into heat.
  Only 1 of light entering the ocean reaches 100m.
• Water displays the selective absorption of light
  with long wavelengths absorbed first and short
  wavelengths absorbed last.
• In the open ocean, blue light penetrates the
  deepest.

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• In turbid coastal waters light rarely penetrates
  deeper than 20m. and the water appears yellow to
  green because particles reflect these
  wavelengths.
• The photic zone is the part of the water column
  penetrated by sunlight.
• The aphotic zone is the part of the water column
  below light penetration and permanently dark.

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The speed of sound in water increases as
salinity, temperature and pressure increase, but
in the ocean, the speed of sound is mainly a
function of temperature and pressure.
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• Above the pycnocline increasing pressure with
  depth increases the speed of sound despite the
  gradual decrease in temperature.
• Within the pycnocline, the speed of sound
  decreases rapidly because of the rapid decrease
  in temperature and only slight increase in
  pressure.
• Below the pycnocline the speed of sound gradually
  increases because pressure continues to increase,
  but temperature only declines slightly.

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• SOFAR Channel is located where sound speed is at
  a minimum. Refraction of sound waves within the
  channel prevents dispersion of the sound energy
  and sound waves travel for 1000s of kilometers
  within the channel.

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SOund Fixing And Ranging floats (SOFAR),
subsurface floats used since the mid 1970s that
freely drift at prescribed pressures. These
provide direct measurements of the ocean
circulation by sending acoustic pulses, typically
at 300 MHz, once a day which can be used to
calculate their positions from their Times of
Arrivals (TOAs) at listening stations moored near
the SOFAR channel depth at known geographical
positions.